In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. High energy protons that are currently being used to treat tumors exploit the proton's relative advantageous dose deposition characteristics. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose as a difference to x-rays. High energy x-rays dose deposition diminishes the further the x-rays penetrate the material. To achieve higher dose to the tumor, multiple photon beams are used. Protons, in contrast, the maximum dose inside the material can reach a maximum for a single beam (i.e., “Bragg peak”) and is controllable by changing the proton energy, something that is impossible to achieve with xrays. In other words one can deliver higher dose to tumors but with lower does to sensitive normal tissues. This can result in better cures with lower toxicity to normal tissues.
Due to the Bragg peak, high energy (mega electron volts) protons more selectively deliver maximal doses into desired areas with reduced radiation at the distal and proximal regions relative to photons. The Bragg peak can be sharp (<1 cm). The proton beams may be broadened using energy modulation to cover larger tumors both distally and proximally. The modulated proton beam is known as a Spread Out Bragg Peak (SOPB). The high dose regions are attributed to protons slowing down near the end of the range. These slowing protons deliver doses within a short distance and can yield a high Linear Energy Transfer (LET). The high rate of energy deposition within short distances has been correlated with high biological lethality. Previously, the LET was only measured at a given fixed point and the LET spatial distribution was inferred from calculations.
Treatment planning controls how patients are treated. Currently treatment planning systems do not use LET information, just dose. The treatment planning systems only compute the physical dose and the biological effect is inferred from clinical experience. But for high LET particles (e.g., distal edge of proton Bragg peak, ion beams), the biological response is quite dependent on the LET. Previously, there was no measurement of LET over an area so conventionally therapy avoids this entire issue and is forced to be performed conservatively because it is unexplored and unknown.